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My 2003 Passat B5 TDI with 6-speed gearbox is making a buzzing/whining(?) noise while driving and it appears as if it comes from under the gear shifter.

The noise is:

  • Dependent on road speed (more audible between 60 kph and 120 kph)
  • Not dependent on engine speed
  • Also audible when gear is in neutral
  • Not dependent on clutch being pressed or not

When accelerating, the noise is there but less audible (probably because the noise of the engine masks it). It is much more audible in neutral or in 4/5/6th gear while decelerating.

Also, when the car is in 4/5/6th gear if I gently press the gear knob up (in 5th) or down (in 4/6th), the noise gets worse.

You can hear the noise in this audio file: http://goo.gl/qXX8x1

Could someone help me diagnosing where the noise is coming from?

I'm ruling out clutch and gearbox because happens in neutral and is not dependent on engine speed. Is this correct?

Could it be the differential? Could it be the U-Joint? Drive shafts?

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    Consider all the different components which always spin relative to the drive wheels, and don't trust where you perceive the sound to be while in the car. Unless it's very loud you won't be able to pinpoint it from within the car. Start with the tires (try a rotation) and work your way up the drive train. Check the wheel bearings and the CV axles. If all of those components are in good shape you could have an issue in your transaxle.
    – Lathejockey81
    Commented Mar 20, 2015 at 0:34
  • Is sound in line with your speed? Not engine speed, but KPH?
    – DucatiKiller
    Commented Mar 20, 2015 at 7:26
  • @DucatiKiller If I understand your question correctly, yes it does. The noise has a higher pitch when increasing the speed and pitch goes down when car is losing speed. I don't know what adjective classifies the noise better but it is a mix of buzzing (caused by some kind of vibration) and a whistling.
    – altosaxwannabe
    Commented Mar 23, 2015 at 14:12

2 Answers 2

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While it is difficult to diagnose car sounds over the Internet, I would say pretty confidently that the sound is coming from the transmission for the reasons below;

You have stated that the pitch of the sound follows the speed of the vehicle, which would lead me to believe this is specifically the final drive or 'differential' (inside the transmission on a transaxle) rather than a specific gear that is causing the noise.

If the vehicle is moving, the final drive is moving. Specific gears or neutral makes no difference.

Under acceleration the output-to-final drive gears are meshing on the 'leading' side of the teeth, which makes a specific sound. Under deceleration they are meshing on the 'trailing' side of the teeth which makes a different (usually louder) specific sound. The sound is created by the two gears being too far apart (like tenths or hundredths of a Millimeter) - see 'backlash' http://en.wikipedia.org/wiki/Backlash_%28engineering%29

Different car speeds (and thus, frequencies of the gears teeth meshing) will increase and decrease the intensity of the sound as it passes through different 'Harmonics' - http://en.wikipedia.org/wiki/Harmonic. Around 90kph (55mph) seems to be a fairly common speed to hear intense harmonics, which is right in the middle of your 'more audible' range.

Pushing on the shifter can preload things inside the transmission and by way of transference is pulling the aforementioned gears apart increasing the backlash, thereby increasing the noise.

The final drive is usually close to the middle of the car, near the shifter.

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    I just realized this car also came in an All Wheel Drive option. If you have AWD this could also be the rear differential, although you're hearing the sound up front so I wouldn't think so.
    – Nick G
    Commented May 27, 2015 at 23:00
  • I am very much inclined to think it is the differential bearing as I can see it's a common problem on this particular vehicle model. This is not a 4wd so it has no rear differential. I haven't found a reliable mechanic that I can trust to diagnose this unfortunately.... One thing is intriguing me though. The noise seems to be "interrupted" by the road layout (e.g. bumps, depressions, etc) causing a slight interruption/change on the noise, particularly when decelerating. I don't know if this car has center bearing on the driveshafts but do you think it could cause this kind of noise as well?
    – altosaxwannabe
    Commented May 30, 2015 at 20:48
  • Yes, the road surface can certainly affect the noise. The easiest way to think of this is in terms of the pressure between the 2 differential gears. On a smooth road under deceleration this pressure is perfectly constant (for sake of this example). Alternatively this pressure can fluctuate (altering or momentarily eliminating the noise produced) as the vehicles weight pushes or pulls against the drivetrain in response to the road.
    – Nick G
    Commented Jun 1, 2015 at 18:19
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    Finally got confirmation that the noise is coming from the gearbox so it's either output shaft or (more likely) differential bearings as this is a common complaint for this 6 speed gearbox. Will have to get it repaired at a transmission specialist.
    – altosaxwannabe
    Commented Aug 25, 2015 at 13:26
  • Sorry to hear that my suspicions were correct since this means an expensive repair for you :( . I would highly suggest a full transmission rebuild, not just replacing the culprit bearings. Microscopic metal flakes usually get created when you start hearing bearing noise and I would bet that the rest of the bearing/gear surfaces are not in too great of shape either.
    – Nick G
    Commented Aug 31, 2015 at 22:31
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Finally got confirmation that the noise is coming from the gearbox so it's either output shaft or (more likely) differential bearings as this is a common complaint for this 6 speed gearbox. Will have to get it repaired at a transmission specialist.

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